The present invention generally relates to color video signal transmitting apparatuses, and more particularly to a color video signal transmitting apparatus supplied in parallel with a time base compressed luminance signal and a time base compressed line-sequential color difference signal which have the same time base compression rate and are obtained by shortening a horizontal scanning period of a television camera compared to a horizontal scanning period which is required to obtain a standard system video signal, for time-division-multiplexing a signal which is obtained by subjecting the time base compressed line-sequential color difference signal to a further time base compression with the time base compressed luminance signal and with a synchronizing signal which is generated independently, to transmit the time-division-multiplexed signal, and for transmitting the time-division-multiplexed signal so that a picture which is reproduced from the time-division-multiplexed signal can be monitored in an electronic viewfinder.
Among the existing color video signal recording and reproducing apparatuses such as video tape recorders (VTRs), the more popular recording and reproducing apparatuses separate a luminance signal and a carrier chrominance signal from a standard system composite color video signal. The standard system is a system such as the NTSC system, the PAL system, and the SECAM system. The separated luminance signal is frequency-modulated, and the separated carrier chrominance signal is frequency-converted into a low frequency range. The frequency converted carrier chrominance signal is frequency-division-multiplexed with the frequency modulated luminance signal and recorded on a recording medium. At the time of the reproduction, a signal processing opposite to the signal processing carried out at the time of the recording, is carried out to obtain a reproduced composite color video signal which is in conformance with the original standard system. In other words, the more popular recording and reproducing apparatuses employ the so-called low-band-conversion recording and reproducing system.
Other various recording and reproducing systems have been proposed besides the low-band-conversion recording and reproducing system. For example, there was a proposed recording and reproducing apparatus which was designed to subject two kinds of color difference signals which are obtained by frequency-demodulating the carrier chrominance signal to a time base compression, and also subject the luminance signal to a time base compression. According to this proposed recording and reproducing apparatus, the time base compressed signals are time-division-multiplexed, and the time division multiplexed signal is frequency-modulated and recorded on the recording medium. At the time of the reproduction, a signal processing opposite to the signal processing carried out at the time of the recording, is carried out to obtain a reproduced composite color video signal which is in conformance with the original standard system. An example of such a recording and reproducing apparatus may be found in the U.S. Pat. Nos. 3,781,463 and No. 4,245,235, for example. This proposed recording and reproducing apparatus takes into account the difference in the bands of the luminance signal and the color difference signals, and takes measures so that the color difference signals having the narrower band can be transmitted within the horizontal blanking period. In other words, one of the color difference signals which is transmitted within one horizontal scanning period (1H), is subjected to a time base compression into approximately 20% of 1H. In addition, to utilize the band effectively, the luminance signal is subjected to a time base compression into approximately 80% of 1H so as to occupy a band which is in the same range as the band of the time base compressed color difference signal, and transmitted. Further, the two color difference signals are time-division-multiplexed, as a line-sequential signal in which the two color difference signals are alternately transmitted for every 1H, with the time base compressed luminance signal. This time-division-multiplexed signal is supplied to a frequency modulator, and an output signal of the frequency modulator is recorded on the recording medium. At the time of the reproduction, a signal processing opposite to the signal processing carried out at the time of the recording, is carried out to obtain a reproduced composite color video signal. The recording and reproducing system employed in this proposed recording and reproducing apparatus, will hereinafter be referred to as a timeplex system.
According to the timeplex system which transmits the time-division-multiplexed signal, there is no duration in which the luminance signal and the color difference signal are transmitted simultaneously. In the case of the NTSC system color video signal and the
system color video signal, a mutual interference and moire may occur between the luminance signal and the color difference signals, because the luminance signal and the carrier chrominance signal are band-share-multiplexed and transmitted. However, such a mutual interference and moire will not occur according to the timeplex system. In addition, even when the color video signal of any one of the NTSC system, the PAL system, and the SECAM system is recorded by an azimuth recording and reproducing system on tracks having the horizontal synchronizing signals recorded in non-alignment between mutually adjacent tracks and then reproduced, there is substantially no crosstalk from the adjacent tracks due to the azimuth loss effect, and it is possible to obtain a reproduced picture of a high picture quality. This is because the time-division-multiplexed signal is recorded on the adjacent tracks in the form of a frequency modulated signal which is obtained by frequency-modulating by the time-division-multiplexed signal a high-frequency carrier which has a large azimuth loss effect.
The time base compressed luminance signal and the time base compressed color difference signal employed in the timeplex system, both have an energy distribution in which the energy is large in the low frequency range and the energy is small in the high frequency range. In other words, the time base compressed luminance signal and the time base compressed color difference signal assume a signal format which is suited for the frequency modulation. Thus, it is possible to obtain a large modulation index, and the signal-to-noise ratio can be greatly improved. Moreover, it is possible to substantially eliminate a deviation in the reproducing time base when expanding the time base.
When producing the time-division-multiplexed signal of the timeplex system described above according to the conventional method, the luminance signal and the carrier chrominance signal were separated from a standard system color video signal. The standard system is a system such as the NTSC, PAL, or SECAM system. The separated carrier chrominance signal was demodulated into two kinds of color difference signals. The separated luminance signal and the two kinds of color difference signals were independently subjected to a time base compression, and were then time-division-multiplexed. As is well known, the frequency band of the luminance signal is considerably wide compared to the frequency band of the color difference signals. Thus, according to the conventional method, memory circuits for subjecting the luminance signal to the time base compression and memory circuits for subjecting the time base compressed luminance signal to a time base expansion so as to return the time base compressed luminance signal to an original time base, had to have a large memory capacity. Further, a circuit part in the time base compressing system for time base compressing the signal to approximately 80% of the video duration, and a circuit part in the time base expanding system for time base expanding the signal back to the original time base, each required a pair of memory circuits which independently carried out the write-in operation and the read-out operation. As a result, there were problems in that the circuit construction became complex, and that the manufacturing cost of the circuit became high.
Another conventional method of producing the time-division-multiplexed signal of the timeplex system, is disclosed in a West German Published Patent Application No. P26 19 027.2. According to this other conventional method, the scanning of a pickup tube for obtaining the color information in a television camera, was performed within a horizontal blanking period of the scanning of a pickup tube for obtaining the luminance information, in order to obtain the time-division-multiplexed signal. However, according to this other conventional method, a deflection current waveform in the pickup tube for obtaining the color information in the television camera, had to be different from a deflection current waveform in the pickup tube for obtaining the luminance information. Consequently, there was a problem in that the construction of the circuit became complex.